Conventionally known resist materials are generally polymeric materials capable of forming amorphous thin film. For example, a solution of a polymeric resist material such as polymethyl methacrylate, polyhydroxystyrene having an acid-dissociating reactive group and polyalkyl methacrylate is applied on a substrate to form a thin resist film, which is then irradiated with ultraviolet rays, far ultraviolet rays, electron beams, extreme ultraviolet rays (EUV), X-rays, etc., to form line patterns having a width of about 45 to 100 nm.
The polymeric resist compounds generally have a molecular weight as large as about 10,000 to 100,000 and a broad molecular weight distribution. Therefore, in a lithographic fine process using the polymeric resist compounds, the surface of the fine patterns is roughened, thereby making it difficult to control the dimension of patterns and reducing the product yield. Thus, the conventional lithographic techniques using the known polymeric resist materials have limitations in fine processing. To produce finer patterns, there have been proposed various low-molecular resist materials.
For example, there have been proposed a positive-type resist composition mainly composed of a low molecular weight, polynuclear polyphenol compound having at least one phenolic hydroxyl group into which an acid-dissociating functional group is introduced (Patent Document 1) and an alkali-developable, negative-type resist composition mainly composed of a low molecular weight, polynuclear polyphenol compound (Patent Document 2). However, these compositions are insufficient in heat resistance to form resist patterns with deformed shapes.
As a low molecular weight resist material, there have been proposed a positive-type resist composition mainly composed of a low molecular weight, cyclic polyphenol compound having at least one phenolic hydroxyl group into which an acid-dissociating functional group is introduced (Patent Documents 3 to 10 and Non-Patent Documents 1 and 2) and an alkali-developable, negative-type resist composition mainly composed of a low molecular weight, cyclic polyphenol compound (Non-Patent Document 3).
It is expected that these low molecular weight, cyclic polyphenol compounds form resist patterns with a high resolution and a small roughness because of their small molecular sizes. In addition, although the molecular weight is low, the low molecular weight, cyclic polyphenol compound has a high heat resistance because of a rigid cyclic structure in its skeletal structure.
However, known low molecular weight, cyclic polyphenol compounds have several drawbacks such as a low etching resistance, a large outgas, a low solubility in safety solvents used in semiconductor production process, and a poor shape of resist patterns. Therefore, the improvement is still required.
It has been recognized that the homogeneity of the solid component of the positive-type resist composition influences the resolution of resist patterns and the roughness. Therefore, a positive-type resist composition is required to contain the low molecular weight, cyclic polyphenol compound having an acid-dissociating functional group which is structurally highly homogeneous, preferably structurally single. However, a low molecular weight, cyclic polyphenol of a single structure is generally obtained by 100% introduction of the acid-dissociating functional group. Such a low molecular weight, cyclic polyphenol of a single structure reduces the sensitivity of a positive-type resist composition. Thus, a low molecular weight, cyclic polyphenol providing a positive-type resist composition with a high sensitivity has not yet been reported.    Patent Document 1: JP 2005-369761A    Patent Document 2: JP 2005-326838A    Patent Document 3: JP 11-153863A    Patent Document 4: JP 11-322656A    Patent Document 5: JP 2002-328473A    Patent Document 6: JP 2003-321423A    Patent Document 7: JP 2005-170902A    Patent Document 8: JP 2006-276459A    Patent Document 9: JP 2006-276742A    Patent Document 10: JP 2007-8875A    Non-Patent Document 1: Seung Wook Chang et al. “Materials for Future Lithography”, Proc. SPIE, Vol. 5753, p. 1    Non-Patent Document 2: Daniel Bratton et al. “Molecular Glass Resists for Next Generation Lithography”, Proc. SPIE, Vol. 6153, 61531D-1    Non-Patent Document 3: T. Nakayama, M. Nomura, K. Haga, M. Ueda, Bull. Chem. Soc. Jpn., 71, 2979 (1998)